1) Field of the Invention
This invention relates generally to fabrication of a semiconductor device and more particularly to a method for forming an air gap as a low dielectric constant material between conductive lines or interconnects using Buckminsterfullerene as a porogen in an air bridge or dielectric material.
2) Description of the Prior Art
In aluminum and copper damascene BEOL interconnects, the reduction of the RC delay is a key design driver. The introduction of low dielectric constant (low-K) materials is one way of reducing the capacitance of the delay, and thereby reducing the delay. The ideal low-K material for reducing RC delay is air. However, introducing air as the dielectric material between metal lines presents processing difficulties.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering the following patents.
U.S. Pat. No. 5,744,399 (Rostoker et al.) teaches a process for lowering the dielectric constant of an insulating layer by incorporating a fullerene within an organic or an inorganic matrix (e.g. composite layer) This patent teaches that the fullerenes can be removed to form pores which reduce the dielectric constant of the remaining matrix. This patent teaches that the preferred method for removing fullerenes is by using a liquid solvent, although an oxygen plasma is suggested as a possible alternative. However this patent does not disclose or suggest the use of fullerenes in an organic spin-on layer as a sacrificial layer or as a sacrificial layer consisting solely of fullerenes. This patent teaches away from the present invention, teaching that fullerene should be used in a mixture with a matrix material. Nor does this patent disclose or suggest the use of an air bridge. U.S. Pat. No. 5,510,645 (Fitch et al.) teaches a method for forming an air gap using a selective etch process to remove a sacrificial spacer.
U.S. Pat. No. 5,461,003 (Havemann et al.) shows a method for forming an air gap by removing a disposable solid layer, preferably photoresist through a porous dielectric layer using an oxygen plasma.
U.S. Pat. No. 5,750,415 (Gnade et al.) shows a method for forming an air gap by removing a disposable liquid through a porous silica precursor film.
U.S. Pat. No. 5,597,444 (Gilton) shows an etching method using a plasma comprising a mixture of a carbon compound, including buckminsterfullerene, and a halogen.
Buckminsterfullerenes (e.g. fullerenes, bucky balls) are a naturally occurring form of carbon named for Buckminster Fuller, the architect of the geodesic dome. Fullerenes can contain from 32 to 960 carbon atoms, and are all believed to have the structure of a geodesic dome. Sixty-carbon fullerenes and seventy-carbon fullerenes are highly stable molecules.